Hello,
I have noticed that the IFRAME element is placed in the "frames" DTD at W3C.
Normally this element is used inline as the name suggests, so it cannot be used in a site that uses either the "transitional" (loose) or the "strict" DTD. Thus the process of developing standards compliant web sites is impeded by this minor detail.
I submit this issue for further discussion.
Best regards,
Andrei Zlate-Podani